Electron beam devices, in particular a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and/or ion beam devices, in particular a so-called “focused ion beam” (FIB) device, are used to study objects, in order to obtain findings with respect to the properties and behaviors of these objects under specific conditions.
An SEM has an electron beam column, in which a beam generator and an objective lens are arranged. An electron beam is generated by means of the beam generator and focused by the objective lens on an object to be studied. By means of a deflection apparatus, the electron beam (also referred to hereafter as a primary electron beam) is guided in a grid over the surface of the object to be studied. The electrons of the primary electron beam interact with the object. As a result of the interaction, electrons in particular are emitted from the object (so-called secondary electrons) or electrons of the primary electron beam are backscattered (so-called backscatter electrons). Secondary electrons and backscatter electrons form the so-called secondary beam and are detected using a detector. The detector signal generated in this way is used for image generation, for example.
The image obtained using the SEM is a two-dimensional representation of a surface of the object to be studied. To calculate a three-dimensional representation of the object from the two-dimensional representation, two methods are known from the prior art, firstly the so-called stereoscopy method and secondly the so-called multi-detector method.
In the stereoscopy method, an object is positioned in a first position relative to a particle beam. Subsequently thereto, a particle beam is guided onto the object and interaction particles are detected, wherein the detection signals thus obtained are used to generate a first image of the object. Subsequently thereto, the object is moved into a second position relative to the particle beam. This second position is distinguished in that it is typically arranged tilted by 3° to 8° relative to the first position. The particle beam is then in turn guided onto the object and interaction particles are detected to generate a second image of the object. In the stereoscopy method, an algorithm is now used, which identifies first points in the first image and second points, which are identical to the first points, in the second image. Furthermore, the lateral distance of each first point to its associated second point is calculated. Since the first image and the second image are recorded from different positions, the lateral distance (i.e., the difference of the two actually identical points) is not necessarily zero, but rather differs from zero. By means of the lateral distances obtained in this way, by means of the known set angle of the first position relative to the second position, and further geometrically known specifications, it is then possible to calculate extents on the object at the first points or the second points, respectively, in a z-direction.
As explained above, the stereoscopy method is based on the fact that corresponding points are ascertained in the first image and in the second image of the object. This can restrict the application of this method to objects in which a network having differentiable points can be identified and used. Furthermore, it is advisable that eucentric movements are used for positioning the object in the first position and/or the second position.
A further method for generating a three-dimensional illustration of an object by means of a particle beam device is the so-called multi-detector method. In the multi-detector method, in contrast to the stereoscopy method, a particle beam is not fed to the object at various angles, but rather images are prepared by means of a particle beam while employing a plurality of detectors, wherein these detectors are arranged symmetrically about an optical axis of a primary electron beam incident on the object. For example, four detectors are used, which each generate one image of the object. By means of the four generated images, slopes along a first axis (x-axis) and along a second axis (y-axis) are determined on every pixel of a studied surface of the object. By integration of the slopes along the first axis and the second axis, a grid of profiles is obtained, which can be assembled to form a three-dimensional model of the object.
In the multi-detector method, it is disadvantageous that the method is substantially only suitable for objects wherein the surfaces to be studied are continuous and do not have large overlaps of structures, since interaction particles, in the case of a specific angular irradiation, are shielded by such structures from a detector and do not reach the detector.
With respect to the prior art, reference is made, for example, to U.S. Pat. No. 4,912,313 A and to U.S. Pat. No. 5,001,344 A.
Accordingly, it would be desirable to specify a method for operating a particle beam device and/or for analyzing an object in a particle beam device, which is simple and relatively rapid to carry out, in such a manner that a three-dimensional representation of an object is obtained relatively rapidly.